ABSTRACT- The Great Blue Heron is used as a bioindicator of the state of the St. Lawrence River (Quebec, Canada). At five years intervals, selected breeding colonies along the River and its estuary are visited to estimate reproductive success and determine level of contamination. Recent research indicates that PBDE are found in many ecosystems and are increasing in concentration in the Great Lakes which is the source of much of the water of the St.Lawrence River. The levels of brominated flame retardants (polybrominated diphenyl ethers), polychlorinated bornanes (toxaphene) congeners, PCBs and chlorinated pesticides were measured in pools of eggs collected from a total of seven colonies including those along the River as well as one inland reference colony. PBDE levels in Great Blue Heron eggs are comparable to those measured in Herring Gull eggs from the Great Lakes. Information on concentrations of toxaphene in avian species is limited. Toxaphene was detected in Great Blue Heron eggs at levels comparable to chlordane levels while DDT was the predominant OC pesticide. Major toxaphene congeners were octachlorobornanes P26, B8-1412 and P 44, and the nonachlorobornane, P50.